M_pi^2 versus m_q: comparing CP-PACS and UKQCD data to Chiral Perturbation Theory

Abstract

I present a selection of CP-PACS and UKQCD data for the pseudo-Goldstone masses in $N_f=2$ QCD with doubly degenerate quarks. At least the more chiral points should be consistent with Chiral Perturbation Theory for the latter to be useful in an extrapolation to physical masses. I find consistency with the chiral prediction but no striking evidence for chiral logs. Nonetheless, the consistency guarantees that the original estimate, by Gasser and Leutwyler, of the $N_f=2$ QCD low-energy scale $\Lambda_3$ was not entirely wrong.